<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .fu{
            width: 500px;
            height: 300px;
            background-color: blue;
            position: relative;
        }
        .zi{
            width: 100px;
            height: 50px;
            background-color: crimson;
            position: absolute;
            left: 50%;
            margin-left: -50px;
            bottom: 50%;
            margin-bottom: -25px;
        }
    </style>
</head>
<body>
     <div class="fu">
         <div class="zi"></div>
     </div>
</body>
</html>